Legacy converter filter with extended frequency range

ABSTRACT

What is presented is a legacy converter filter. The legacy converter filter comprises a first circuit that operates to substantially pass signals in a first frequency band of approximately 5 to 52 MHz; a second circuit that operates to substantially pass signals in a second frequency band of approximately 85 MHz to 2 GHz; and a third circuit that operates to substantially block signals in a third frequency band of approximately 52 MHz to 85 MHz.

BACKGROUND OF THE INVENTION

The present invention relates to legacy converter filters, and more particularly relates to a legacy converter filter that includes a bandstop filter portion to protect the input circuits of the legacy converter boxes.

Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV (CATV) system. It is employed by many cable television operators to provide Internet access over their existing hybrid fiber-coaxial (HFC) infrastructure. In many instances DOCSIS is used to provide video content as well as Internet connectivity and telephone service.

As cable companies migrate from earlier versions of DOCSIS (Data Over Cable Service Interface Specification) to DOCSIS 3 and above, the bandwidth requirement for digital services is ever increasing. This is the case especially in the return band (i.e. upstream band) which in prior versions of DOCSIS such as version 3.0 was limited to the band below 42 MHz. The upstream return band frequency in DOCSIS 3.0 modems is 5 to 42 MHz. The DOCSIS 3.1 standard moves the upper return band frequency from 42 MHz to 85 MHz in the United States and up to 200 MHz in countries outside the United States.

An issue is created when increasing the return path upper frequency is the reuse of the frequency band from 42 to 85 MHz, which is utilized in the United States for channels 2 through 6 on TV set top boxes.

A problem thus arises in that legacy converter boxes that receive channels 2 through 6 are now over driven by the higher signal level produced by the DOCSIS 3.1 equipment return path signals. The higher output DOCSIS 3.1 signals overdrive (i.e. overload) the input tuner of the legacy converter boxes.

Cable companies are also concerned about the insertion loss and return loss in the forward band, 54 MHz to 2 GHz and in some cases 3 GHz. This can affect the quality of service for interne and digital channels. Currently the requirement for having good quality service is from 54 MHz to 1002 MHz and is considered to be normal in the industry. Increasing the upper frequency limit to 2000 MHz allows the cable operators to offer more services on an already cramped system.

The present invention overcomes this problem by providing a legacy converter filter that includes a bandstop filter portion to protect the input circuits of the legacy converter boxes. The legacy converter filter also functions to pass the forward path (54 MHz to 2 GHz) with minimal loss and reflection.

SUMMARY OF THE INVENTION

The present invention relates to a legacy converter filter. More particularly, in one aspect, the invention comprises a circuit that operates to substantially pass signals between a plurality of frequency bands widths and block frequencies at other band widths. The legacy converter filter comprises a first circuit that operates to substantially pass signals in a first frequency band of approximately 5 to 52 MHz, a second circuit that operates to substantially pass signals in a second frequency band of approximately 85 MHz to 2 GHz, and a third circuit that operates to substantially block signals in a third frequency band of approximately 52 MHz to 85 MHz.

In one embodiment of this invention, the first circuit comprises a plurality of capacitors operating in parallel with a plurality of inductors. In another embodiment, the second circuit comprises a plurality of capacitors operatively connected to a plurality of inductors and each capacitor being connected to ground. In a further embodiment, the third circuit comprises a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to a inductor and ground. In this embodiment, or a similar embodiment, a resistor can be operatively connected to the first set of capacitors. Also in this embodiment, or a similar embodiment, a plurality of resistors could be operatively connected to the first set of capacitors. Also in this embodiment, or a similar embodiment, a capacitor of the first set of capacitors can be configured to be in parallel with a inductor. Also in this embodiment, or a similar embodiment, a capacitor of the first set of capacitors could also be further in series with a resistor that is in parallel with an inductor. Also in this embodiment, or a similar embodiment, a capacitor of the first set of capacitors could also only be in series with a resistor that is in parallel with an inductor. In yet a further embodiment, a resistor is added at the input and the output of the legacy converter filter. In yet a further embodiment, a resistor is added at the output of the legacy converter filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first embodiment of the legacy converter filter;

FIG. 2 exemplifies one aspect of the performance of the converter filter of FIG. 1;

FIG. 3 exemplifies another aspect of the performance of the converter filter of FIG. 1;

FIG. 4 exemplifies another aspect of the performance of the converter filter of FIG. 1;

FIG. 5 illustrates a second embodiment of the converter filter;

FIG. 6 exemplifies one aspect of the performance of the converter filter of FIG. 5;

FIG. 7 exemplifies another aspect of the performance of the converter filter of FIG. 5;

FIG. 8 exemplifies another aspect of the performance of the converter filter of FIG. 5;

FIG. 9 illustrates another embodiment of the converter filter;

FIG. 10 illustrates another embodiment of the converter filter;

FIG. 11 illustrates another embodiment of the converter filter;

FIG. 12 illustrates another embodiment of the converter filter;

FIG. 13 illustrates another embodiment of the converter filter;

FIG. 14 illustrates another embodiment of the converter filter;

FIG. 15 illustrates another embodiment of the converter filter;

FIG. 16 illustrates another embodiment of the converter filter;

FIG. 17 illustrates another embodiment of the converter filter;

FIG. 18 illustrates another embodiment of the converter filter;

FIG. 19 illustrates another embodiment of the converter filter;

FIG. 20 illustrates another embodiment of the converter filter;

FIG. 21 illustrates another embodiment of the converter filter; and

FIG. 22 shows a typical home cable network environment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It is well known in the cable industry that impedance, Second Resonant Frequency (SRF), fringing capacitance, etc., limit the performance of the system at higher frequencies. By removing four circuit elements and replacing two of them with resistor values from 0 to 75 Ohm a significant improvement in insertion and return loss was achieved. By adding the resistances to one leg of the filter a better match between the two branches and the input or output are achieved. The same is true when the components on the input side are changed in similar fashion.

In one embodiment, the legacy converter filter is placed up line from legacy converter boxes, i.e. TV set top boxes (as shown in FIG. 22). Since the path to DOCSIS 3.1 modems cannot be blocked, the filter is preferably placed in front of the legacy converter boxes they are meant to protect as opposed to other upstream or downstream locations.

Referring to the drawings in detail, and specifically to FIG. 1, reference numeral 10 generally designates an exemplary converter filter having a low pass portion and a high pass portion in accordance with an embodiment of the present invention. Communications enter the converter filter at the input 1 and go to the legacy converter boxes (or other such similar devices) by exiting the circuit 10 at the output 2. The converter filter 10 includes a first circuit portion 12, second circuit portion 14, and a third circuit portion 16. The first circuit portion 12 comprises capacitors C2, C4, and C6. The second circuit portion 14 comprises a plurality of inductors L1, L2, L3, L4, and L5 as well as a plurality capacitors C1, C3, C5, and C7. The third circuit portion 16 comprises a plurality of inductors L6, L7, L8, L9, L11 and L12 as well as plurality of capacitors C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, and C20. Each of the inductors and capacitors of the converter filter 10 operate in conjunction with each other to substantially pass signals in a first frequency band and a second frequency band and to substantially block signals in a third frequency band. The performance of the circuit of FIG. 1 is shown in FIGS. 2, 3 and 4, in which a skilled artisan will better understand the specific frequencies being filtered.

FIG. 5 illustrates a second embodiment of the converter filter 10. The performance of the circuit of FIG. 2 is shown in FIGS. 6, 7 and 8. It is noted that the embodiment of the circuit 10 of FIG. 5 removes capacitors C18, C19, C20 and choke L11 and replaces them with two resistors R1 and R2, which may be combined to a single resistor R3 (not shown). It should be understood that a preferable range of values for R1 and R2 is from 0 to 10 Ohms each, e.g., R1=0 Ohms and R2=2.7 Ohms or the equivalent thereof.

It is noted that the performance of the circuit of FIG. 5 is improved over that of the embodiment shown in FIG. 1. In particular, the passband response shown in FIG. 7 as compared to that of FIG. 3 now extends out to 2 GHz and, for example, at 1700 MHz provides an almost 3 dB improvement. Considering the return loss performance shown in FIGS. 4 and 8, the second embodiment circuit provides a nearly 15 dB improvement at 1700 MHz.

Going from the circuit of FIG. 1 to that of FIG. 5 was achieved by replacing three capacitors and a choke inductor with one or two resistors. An advantage of the circuit of FIG. 5 is that the resistors are far less expensive than capacitors and choke inductors. The insertion of R2 into the circuit resulted in better matching of the passband and removing the other elements C18, C19, C20 and L11 helped improve the performance in the passband. In particular, replacing the inductor with a resister improved the performance in the higher end of the frequency range. C20 is replaced with inductor to match but only for lower frequencies. Thus, the improved circuit of FIG. 5 functions to extend the passband and improve circuit performance along with achieving a reduction in parts and related bill of material cost reduction.

As an example, nominal values for the components in the circuits of FIGS. 1 and 5 are as presented below in Table 1:

TABLE 1 L1 .22 uH Nominal L2 .33 uH C1  62 NPO L3 .22 uH C2 omit L4 .33 uH C3  56 NPO L5 .22 uH C4  20 NPO L6 15 nH C5  62 NPO L7 22 nH C6 omit L8 27 nH C7  62 NPO L9 36 nH C8 9.1 NPO L10 18 nH C9  22 NPO L11 omit C10 3.3 NPO Clr. Bd. 441 C11 4.7 NPO C12 4.7 NPO C13 3.3 NPO C14 7.5 NPO C15 2.4 NPO C16 6.2 NPO C17  10 NPO C18 6.8 NPO C19 omit C20 4.3 nH 

Referring now to FIG. 9, what is disclosed is a filter circuit similar to that of the embodiment of FIG. 5 with capacitors C8, C9, C10 and choke L6 replaced with resistors R1 and R2 (i.e. the components on the input side of the circuit rather than the output side).

FIG. 10 shows an alternative embodiment of the filter circuit with capacitor C12 removed rather than C10. FIG. 11 shows an alternative embodiment of the filter circuit, with capacitor C14 removed rather than C10. FIG. 12 shows an alternative embodiment of the filter circuit, with capacitor C21 added to the circuit, in parallel with choke L11 and choke L12 added to the circuit. FIG. 13 shows an alternative embodiment of the filter circuit with resistor R1 added to the circuit, in parallel with choke L 11, and choke L12 added to the circuit. FIG. 14 shows an alternative embodiment of the filter circuit with resistor R1 added to the circuit in parallel with choke L11.

FIG. 15 shows an alternative filter circuit, with resistor R1 added to the circuit in series with choke L11 and capacitor C19. FIG. 16 shows an alternative embodiment of the filter circuit with resistor R1 added to the circuit in series with choke L11 and capacitor C19 removed. FIG. 17 shows an alternative embodiment of the filter circuit, with resistor R1 added to the circuit in series with capacitor C19 and choke L11 removed. FIG. 18 shows an alternative embodiment of the filter circuit, with capacitor C19 and choke L11 replaced with resistor R1. FIG. 19 shows an alternative embodiment of the filter circuit, with resistors R1 and R2 added to the low pass filter instead of the high pass filter. FIG. 20 shows an alternative embodiment of the filter circuit, with resistors R1 and R2 added to the input and output of the converter filter. FIG. 21 shows an alternative filter circuit, with resistor R1 added to the output of the converter filter.

Although the invention has been described with reference to preferred embodiments thereof, it is understood that various modifications may be made thereto without departing from the full spirit and scope of the invention as defined by the claims which follow. 

What is claimed is:
 1. A legacy converter filter, comprising: a first circuit operative to substantially pass signals in a first frequency band of approximately 5 to 52 MHz; a second circuit operative to substantially pass signals in a second frequency band of approximately 85 MHz to 2 GHz; and a third circuit operative to substantially block signals in a third frequency band of approximately 52 MHz to 85 MHz.
 2. The legacy converter filter of claim 1 wherein the first circuit comprises a plurality of capacitors operating in parallel with a plurality of inductors.
 3. The legacy converter filter of claim 1 wherein the second circuit comprises a plurality of capacitors operatively connected to a plurality of inductors and each capacitor being connected to ground.
 4. The legacy converter filter of claim 1 wherein the third circuit comprises a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground.
 5. The legacy converter filter of claim 1 wherein the third circuit comprises: a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground; and a resistor operatively connected to the first set of capacitors.
 6. The legacy converter filter of claim 1 wherein the third circuit comprises: a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground; and a plurality of resistors operatively connected to the first set of capacitors.
 7. The legacy converter filter of claim 1 wherein the third circuit comprises: a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground; and wherein at least one capacitor of the first set of capacitors is configured to be in parallel with an inductor.
 8. The legacy converter filter of claim 1 wherein the third circuit comprises: a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground; and wherein at least one capacitor of the first set of capacitors is further in series with a resistor in parallel with an inductor.
 9. The legacy converter filter of claim 1 wherein the third circuit comprises: a first set of capacitors operatively connected to a second set of capacitors and each capacitor of the first set of capacitors being connected in series to an inductor and ground; and wherein at least one capacitor of the first set of capacitors is only in series with a resistor in parallel with an inductor.
 10. The legacy converter filter of claim 1 wherein a resistor is added at the input and the output of the legacy converter filter.
 11. The legacy converter filter of claim 1 wherein a resistor is added at the output of the legacy converter filter. 